hello everyone, im just learning to use my dslr cam and read articles and video regarding dslr cam aperture, shutter speed and iso. i don't know really where to begin i don't want to use the auto mode of my dslr so i am using av mode sometimes i have a nice picture and most of the time overexpose or underexpose. any tips or idea will be appreciated.cheers,alain

There's nothing wrong with using full auto, or P settings, especially while getting a feel for the camera & differing situations. You could always take 1 pic on full auto.....then take another with YOUR settings & see how they compare.

Auto ISO is also a safe option.

Just keep taking MANY many shots & try out all the settings until you're fairly confident. Also, better to slightly under expose (you can lighten in PP) rather than trying to recover blown highlights if over exposed.

I shoot a lot in AV mode and find it a really good way to learn about different photo shooting.

By placing it in AV mode the camera is adjusting the shutter speed dependent upon which aperture setting you are choosing.

An Aperture setting of 4.5-5.6 has a relatively narrow centre of focus whilst upping it to say 22 brings in a wider frame of focus ie more of the photo is in focus, in simple terms anyway, thats how i understand it anyway (i am sure someone can correct - expand on this!!).

Once you have experimented with various aperture settings and seen how the camera adjusts shutter speed then you can start adjusting exposure or even taking bracketed exposure shots (under exposed, normal, over exposed) and see the difference.

I shoot mostly in AV mode and when i have time swith to M mode and play with the settings.

I reckon that 95% of the time I'm using Aperture Priority, or AV, mode. Just because you're not using full Manual doesn't mean you're not using the camera to full effect - far from it.

The times I wouldn't use AV:

Home Studio with FlashEvents where I want to use a set shutter speed - e.g. airshows, motor racing etcNight on a tripodLong exposures on a tripod

You've got a lot to balance - shutter speed, aperture, ISO. AV will let you select the aperture and the camera will set the rest for you (if you use auto ISO). The only thing you'll need to do then is check your histogram and use some +ive or -ive exposure compensation, depending on whether you have blown highlights or lost shadow detail. As the light changes, you'll have to reevaluate your exposure compensation and to start you'll forget to do this, but this is a far easier method than using full manual when you're shooting on the fly.

When you say you're using AV and the camera is under exposing or over exposing, then the issue is your metering modes.

Check your manual or online to find out about the various metering modes your camera offers. For example, if you're taking a photograph of a person who is in shade, yet the background is bright, your subject will appear under exposed if you are using Matrix metering (can't remember the Canon equivalent). Basically your camera is metering the whole scene and taking an average. The bright background will have an effect and therefore your subject will become under exposed. Changing to Centre weighted or Spot metering (again, I can't remember the Canon equivalent) will place more emphasis on the centre of the image or where you are focussing, which will overexpose the background but expose the subject better. Or you could just use +1 - +2 EV and do things that way.

Or the other way - shoot RAW, and then blend two different versions of the same image with different exposure values

Or the other way - use an off camera flash (preferably) or your pop up and balance the exposure that way

If I'm shooting a nightscape then I'll generally use full Manual and shoot in RAW (maybe RAW plus JPG). I use the same technique for long exposures by day. I use the following setup:

Camera on tripod

Compose shot

Dial in required aperture

Camera on timer or using remote shutter release

Camera in full Manual

Auto ISO off - set to lowest possible ISO manually

Liveview zoomed in to focus

Once focus achieved, then switch off autofocus on camera body or lens

Liveview off

Lastly, but perhaps most importantly with long exposures, cover the viewfinder (my D700 has a built in cover) - this is not so important by night, but you want to avoid light leakage

Now generally you use your histogram to help with adjusting your setting to 'expose to the right'. This is a useful thing to do at night also, but you have to bear in mind that you will always have point light sources which will blow out. If your camera is set up using matrix (or evaluative in Canonland?) metering you will have an OK looking scene but your point lightsources and their surrounding areas will be very blown out. You could use AV and dial in some -ive exposure compensation, or you could just dial that in with your inbuilt meter in Manual mode. Different scenes will require different quantities of under exposure, so I tend to use Manual at night and adjust to suit.

Obviously at night you'll have a lot of clipped shadows as well, and a lot of very dark shadows. Simply dialling in -ive EV will make your shadows darker still. Another reason for Manual Mode for me is to quickly bracket my shots so I can then blend them later using Exposure Fusion (a more 'realistic' version of HDR). This is preferred by me to recovering the shadows in Photoshop or Lightroom as that can induce noise. I'll end up with a much cleaner image, an one which represents more of what the eye sees when you are taking the image. An added bonus is the extra micro contrast that this process brings.

Long exposures by day - manual is definitely the way to go. If I'm using a 10 stop ND filter or stacked 3 stop and 10 stop I'll end up with a exposure running into minutes. It that case I'll be in bulb mode, with a remote timer set up and using the setup I mentioned above.

Below are a couple of examples - firstly with 24-70mm f2.8 lens on a D90 - single exposure at night (quite humid so a little humidity haze). In this case I used ISO800 (which was just about the limit for my on the D90) and 0.4 second shutter speed to capture the laser out of the top of the Burj Al Arab which moves around the sky on the hour. The exposure was the best I could manage to balance the scene, and in full manual mode it was quick and easy to move from f8 and ISO 100 to f2.8 and ISO 800 as soon as the laser appeared. Note the blown highlights around the building and palm trees.

Next up, one of my first images with the D700. Same lens (24-70 f2.8 ), but bigger full frame sensor. f11, ISO 200 and 5 images blended using Exposure Fusion in Photomatix Pro. No sharpening has been applied to this image. In full manual it was quick and easy to bracket. In AV it would have been more fiddly. Needless to say I was quite happy with the results, moving to the D700! I find that shooting in RAW is a necessity - with multiple light sources and different colour temperatures, in RAW you have the ability to fine tune your white balance to suit.

Could you at least help me a bit to tell me which software you use? When combining (-2,0,+2 EV) in CS4 and playing with the sliders, I find I can only get a very small bit more DR than when using a single exposure from 0 EV.